Chloroquine reduces neuronal and glial iron uptake

Chloroquine inhibits Rhodococcus equi replication in murine and foal alveolar macrophages by iron-starvation

Rhodococcus equi preferentially infects macrophages causing pyogranulomatous pneumonia in young foals. Both the vapA and rhbC genes are up-regulated in an iron (Fe)-deprived environment, such as that found within macrophages. Chloroquine (CQ) is a drug widely used against malaria that suppresses the intracellular availability of Fe in eukaryotic cells. The main objective of this study was to evaluate the ability of CQ to inhibit replication of virulent R. equi within murine (J774A.1) and foal alveolar macrophages (AMs) and to verify whether the mechanism of inhibition could be Fe-deprivation-dependent. CQ effect on R. equi extracellular survival and toxicity to J774A.1 were evaluated. R. equi survival within J774A.1 and foal AMs was evaluated under CQ (10 and 20μM), bovine saturated transferrin (bHTF), and bovine unsaturated transferrin (bATF) exposure. To explore the action mechanism of CQ, the superoxide anion production, the lysozyme activity, as well as the relative mRNA expression of vapA and rhbC were examined. CQ at≤20μM had no effect on R. equi extracellular multiplication and J774A.1 viability. Exposure to CQ significantly and markedly reduced survival of R. equi within J774A.1 and foal AMs. Treatment with bHTF did not reverse CQ effect on R. equi. Exposure to CQ did not affected superoxide anion production or lysozyme activity, however vapA and rhbC expression was significantly increased. Our results reinforce the hypothesis that intracellular availability of Fe is required for R. equi survival, and our initial hypothesis that CQ can limit replication of R. equi in J774A.1 and foal AMs, most likely by Fe starvation.

Chloroquine inhibits Paracoccidioides brasiliensis survival within human monocytes by limiting the availability of intracellular iron

The mechanisms used by Paracoccidioides brasiliensis(Pb 18) to survive into monocytes are not clear. Cellular iron metabolism is of critical importance to the growth of several intracellular pathogens, including P. brasiliensis, whose capacity to multiply in mononuclear phagocytes is dependent on the availability of intracellular iron. Chloroquine, by virtue of its basic properties, has been shown to prevent release of iron from holotransferrin by raising endocytic and lysosomal pH, and thereby interfering with normal iron metabolism. Then, in view of this, we have studied the effects of CHLOR on P. brasiliensis multiplication in human monocytes and its effect on the murine paracoccidioidomycosis. CHLOR induced human monocytes to kill P. brasiliensis. The effect of CHLOR was reversed by FeNTA, an iron compound that is soluble at neutral to alkaline pH, but not by holotransferrin, which releases iron only in an acidic environment. CHLOR treatment of Pb 18-infected BALB/c mice significantly reduced the viable fungi recovery from lungs, during three different periods of evaluation, in a dose-dependent manner. This study demonstrates that iron is of critical importance to the survival of P. brasiliensis yeasts within human monocytes and the CHLOR treatment in vitro induces Pb 18 yeast-killing by monocytes by restricting the availability of intracellular iron. Besides, the CHLOR treatment in vivo significantly reduces the number of organisms in the lungs of Pb-infected mice protecting them from several infections. Thus, CHLOR was effective in the treatment of murine paracoccidioidomycosis, suggesting the potential use of this drug in patients' treatment.

Expression of transferrin mRNA in rat oligodendrocytes is iron-independent and changes with increasing age

As transferrin in the brain may originate principally from synthesis by three different cell types, i.e. hepatocytes, oligodendrocytes and choroid plexus, this study employed a morphological analysis to specifically address oligodendrocytic expression of transferrin mRNA in young (P17) and adult (P50) rats. In spite of a lowering of the concentration of brain iron by approximately 22% in the young iron deficient rats transferrin mRNA expression in oligodendrocytes was not affected when measured by quantitative densitometry. In adult rats, the baseline transferrin mRNA expression in oligodendrocytes was higher than in the young animals, but did not change in spite of a reduction in brain iron by approximately 19%. Brain iron and transferrin mRNA expression in oligodendrocytes were unaltered in iron overloaded rats when compared to age-matched controls. As transferrin expression was lower in the young rat, when constituents from the blood have a relatively higher concentration in the brain than during adulthood, it seems unlikely that blood-borne factors such as transition metals act as inducers of transferrin gene expression in oligodendrocytes. Instead, the higher but constitutive expression of transferrin mRNA at later ages, when the blood-brain barrier segregates the brain from other body parts, may indicate that molecules released from the brain interior are responsible for regulating transcription of the transferrin gene.

Relationship between chloroquine toxicity and iron acquisition in Saccharomyces cerevisiae

Chloroquine is one of the most effective antimalarials, but resistance to it is becoming widespread. However, we do not fully understand either the drug's mode of action or the mechanism of resistance. In an effort to expand our understanding of the mechanism of action and resistance associated with chloroquine, we used Saccharomyces cerevisiae as a model eukaryotic system. To aid in the discovery of potential drug targets we applied the transcriptional profiling method to identify genes transcriptionally responsive to chloroquine treatment in S. cerevisiae. Among the genes that were differentially expressed with chloroquine treatment were a number of metal transporters involved in iron acquisition (SIT1, ARN2, ARN4, and SMF2). These genes exhibit similar expression patterns, and several are known to be regulated by AFT1, a DNA binding protein, which responds to iron levels in the cell. We investigated the role of chloroquine in iron metabolism by using a variety of approaches, including pharmacological, genetic, and biochemical techniques. For these experiments, we utilized yeast lacking the major iron uptake pathways (FET3 and FET4) and yeast deficient in SIT1, encoding the major up-regulated iron siderophore transporter. Our experiments show that yeast genetically or environmentally limited in iron availability has increased sensitivity to chloroquine in pharmacological assays and that the addition of iron rescues these cells from chloroquine killing. 55FeCl3 accumulation was inhibited in the presence of chloroquine, and kinetic analysis demonstrated that inhibition was competitive. These results are consistent with deprivation of iron as a mechanism of chloroquine killing in yeast.

Transferrin and transferrin receptor function in brain barrier systems

1. Iron (Fe) is an essential component of virtually all types of cells and organisms. In plasma and interstitial fluids, Fe is carried by transferrin. Iron-containing transferrin has a high affinity for the transferrin receptor, which is present on all cells with a requirement for Fe. The degree of expression of transferrin receptors on most types of cells is determined by the level of Fe supply and their rate of proliferation. 2. The brain, like other organs, requires Fe for metabolic processes and suffers from disturbed function when a Fe deficiency or excess occurs. Hence, the transport of Fe across brain barrier systems must be regulated. The interaction between transferrin and transferrin receptor appears to serve this function in the blood-brain, blood-CSF, and cellular-plasmalemma barriers. Transferrin is present in blood plasma and brain extracellular fluids, and the transferrin receptor is present on brain capillary endothelial cells, choroid plexus epithelial cells, neurons, and probably also glial cells. 3. The rate of Fe transport from plasma to brain is developmentally regulated, peaking in the first few weeks of postnatal life in the rat, after which it decreases rapidly to low values. Two mechanisms for Fe transport across the blood-brain barrier have been proposed. One is that the Fe-transferrin complex is transported intact across the capillary wall by receptor-mediated transcytosis. In the second, Fe transport is the result of receptor-mediated endocytosis of Fe-transferrin by capillary endothelial cells, followed by release of Fe from transferrin within the cell, recycling of transferrin to the blood, and transport of Fe into the brain. Current evidence indicates that although some transcytosis of transferrin does occur, the amount is quantitatively insufficient to account for the rate of Fe transport, and the majority of Fe transport probably occurs by the second of the above mechanisms. 4. An additional route of Fe and transferrin transport from the blood to the brain is via the blood-CSF barrier and from the CSF into the brain. Iron-containing transferrin is transported through the blood-CSF barrier by a mechanism that appears to be regulated by developmental stage and iron status. The transfer of transferrin from blood to CSF is higher than that of albumin, which may be due to the presence of transferrin receptors on choroid plexus epithelial cells so that transferrin can be transported across the cells by a receptor-mediated process as well as by nonselective mechanisms. 5. Transferrin receptors have been detected in neurons in vivo and in cultured glial cells. Transferrin is present in the brain interstitial fluid, and it is generally assumed that Fe which transverses the blood-brain barrier is rapidly bound by brain transferrin and can then be taken up by receptor-mediated endocytosis in brain cells. The uptake of transferrin-bound Fe by neurons and glial cells is probably regulated by the number of transferrin receptors present on cells, which changes during development and in conditions with an altered iron status. 6. This review focuses on the information available on the functions of transferrin and transferrin receptor with respect to Fe transport across the blood-brain and blood-CSF barriers and the cell membranes of neurons and glial cells.

Cellular distribution of iron in the brain of the Belgrade rat

In this study, we investigated the cellular distribution of iron in the brain of Belgrade rats. These rats have a mutation in Divalent Metal Transporter 1, which has been implicated in iron transport from endosomes. The Belgrade rats have iron-positive pyramidal neurons, but these are fewer in number and less intensely stained than in controls. In the white matter, iron is normally present in patches of intensely iron-stained oligodendrocytes and myelin, but there is dramatically less iron staining in the Belgrade rat. Those oligodendrocytes that stained for iron did so strongly and were associated with blood vessels. Astrocytic iron staining was seen in the cerebral cortex for both normal rats and Belgrade rats, but the iron-stained astrocytes were less numerous in the mutants. Iron staining in tanycytes, modified astrocytes coursing from the third ventricle to the hypothalamus, was not affected in the Belgrade rat, but was affected by diet. The results of this study indicate that Divalent Metal Transporter 1 is important to iron transport in the brain. Iron is essential in the brain for basic metabolic processes such as heme formation, neurotransmitter production and ATP synthesis. Excess brain iron is associated with a number of common neurodegenerative diseases. Consequently, elucidating the mechanisms of brain iron delivery is critical for understanding the role of iron in pathological conditions.

Cerebellar granule cells acquire transferrin-free iron by a carrier-mediated process

In this study, the mechanism of transferrin-free iron uptake by brain neuronal cells was investigated using the cultured cerebellar granule cells. Effects of incubation time, iron concentration, temperature and other divalent metals on the cellular uptake were determined. After five days of plating, the cells were incubated with different concentrations of transferrin-free iron in isotonic sucrose solution at different temperatures for a certain time. The cellular transferrin-free iron uptake was analysed by measuring the cellular radioactivity with a gamma-counter. The result showed that the cultured cerebellar granule cells had the capacity to acquire transferrin-free iron at pH 6.5, at which it was demonstrated that transferrin binds iron very poorly and only very little transferrin can be internalized by reticulocytes and HeLa cells. The iron uptake by cells increased with incubation time in a linear manner at a rate of 0.1076 pmol/microg protein/min within the first 10 min. The uptake was time- and temperature-dependent, iron concentration saturable, and inhibited by several divalent metal ions, such as Co2+, Zn2+, Mn2+ and Ni2+. These characteristics of transferrin-free iron uptake by the cultured cerebellar granule cells observed in this study, similar to those obtained from cells outside of the brain, implied that a carrier-mediated iron transport system might be present on the membrane of this type of brain neuronal cells. In addition, no significant difference in malondialdehyde measurement was found when the cells were incubated without or with the lower concentrations of iron (< 4 microM) for 20 min at 37 degrees C, demonstrating that this system was valid for studying membrane iron transport in this type of brain neuronal cell.

Effect of chronic chloroquine administration on iron loading in the liver and reticuloendothelial system and on oxidative responses by the alveolar macrophages

The ability of chloroquine to alter iron loading in the liver, spleen, and alveolar macrophages was investigated in iron-loaded or -depleted rats. Chloroquine significantly reduced incorporation of iron into the liver, spleen, and alveolar macrophages of animals loaded in vivo with iron dextran. The ability of these macrophages to respond to oxidative stress was assayed by their capacity to release reactive nitrogen intermediates after lipopolysaccharide (LPS) stimulation. A significant reduction in nitrite release was observed in primary cultures of macrophages isolated from chloroquine/iron dextran-administered rats in comparison to macrophages lavaged from rats iron-loaded alone. Macrophages isolated from iron-deficient rats showed a significant increase in nitrite after LPS stimulation, whereas nitrite release in the macrophages lavaged from the rats which had also received chloroquine during the iron depletion regime was much lower. These results indicate that the use of agents which decrease the iron content and diminish the oxidative response of the cell to altered iron status may be of therapeutic value in patients with iron loading, particularly of the reticuloendothelial system.

Aluminum alters iron and manganese uptake and regulation of surface transferrin receptors in primary rat oligodendrocyte cultures

Transferrin (Tf) is a major transport protein for both iron (Fe) and aluminum (Al), as well as manganese (Mn) and it can mediate cellular uptake of these elements via cell surface Tf receptors. To study the effect of Al-Tf on Tf receptor regulation, primary oligodendrocyte cultures were prepared from cortices of newborn rats. The effects of Al-Tf on 54Mn and 59Fe uptake were compared to those of apo-, Fe-, or Mn-Tf (1.25 microM). To examine changes in cell surface Tf binding capacity, preincubation (4 h, 37 degrees C) was performed with apo-, Al- or Fe-Tf and homologous receptor binding studies were subsequently conducted with 125I-Fe-Tf at 4 degrees C. Incubation with Al-Tf, but not with equimolar amounts of Al chloride or Al citrate, led to dose-related increases in cellular Al. Incubation with either Al- or Fe-Tf decreased 59Fe uptake, while incubation with either Al- or Mn-Tf decreased 54Mn uptake. Surface Tf receptor sites/cell were 1.05, 0.60 and 0.46 x 10(5) after incubations with equivalent amounts of apo-, Fe-, and Al-Tf respectively. The data suggest that Al-Tf down-regulates surface Tf receptors on oligodendrocytes and can limit Fe and Mn uptake through this mechanism.

Inhibition of growth of Histoplasma capsulatum yeast cells in human macrophages by the iron chelator VUF 8514 and comparison of VUF 8514 with deferoxamine

Histoplasma capsulatum requires intracellular iron to survive and multiply within human and murine macrophages (M phi). Thus, iron chelators may be useful compounds in the treatment of histoplasmosis. In the present study we compared the efficacies of five different iron chelators with deferoxamine (DEF) for their capacity to inhibit the growth of H. capsulatum yeast cells in culture medium and within human M phi. Of the agents tested, only one, VUF 8514, a 2,2'-bipyridyl analog, was found to be effective. VUF 8514 inhibited the growth of yeast cells in tissue culture medium and within M phi in a dose-response fashion. In tissue culture medium, the 50% effective dose (ED50) of VUF 8514 was 30 nM and the ED50 of DEF was 1 mM. In human M phi, the ED50 of VUF 8514 was 520 nM and the ED50 of DEF was 4 mM. Thus, VUF 8514 was effective at a concentration 7.7 x 10(3)-fold lower than DEF in inhibiting the growth of yeast cells in M phi. Inhibition of the intracellular growth of yeast cells by VUF 8514 was reversed by holotransferrin and iron nitriloacetate, an iron compound that is soluble at neutral to alkaline pH. Thus, VUF 8514 inhibits the intracellular growth of yeast cells by acting as an iron chelator rather than through its capacity as a weak base. These data suggest that the hydroxamic acid siderophore of H. capsulatum yeast cells competes successfully for iron against some iron chelators but not others and that VUF 8514 may be a potential therapeutic agent for the treatment of histoplasmosis.

Therapeutic brain concentration of the NMDA receptor antagonist amantadine

Amantadine (1-amino-adamantane) is clinically used for the management of Parkinson's disease and drug-induced extrapyramidal symptoms. It has previously been shown that amantadine is a low-affinity uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist with rapid blocking and unblocking channel kinetics (Ki-value at the PCP binding site = 10 microM). The aim of the present studies was to estimate concentrations of amantadine in the central nervous system under therapeutic conditions. In homogenates of postmortem human brain tissue the amantadine concentration appeared to be homogeneously distributed over a wide range of brain areas. Amantadine concentration increased with duration of treatment and decreased wit drug-free time. When the duration of treatment was > or = 10 days and drug-free time < or = 3 days, mean amantadine concentrations in postmortem brain tissue ranged from 48.2 to 386 microM. In contrast to brain tissue, amantadine concentration in cerebrospinal fluid (CSF) and serum was in the low micromolar range ( < 17 microM). CSF and serum total values were highly correlated to each other and were always lower in CSF. The mean CSF/serum ratio for total amantadine was 0.76. To further estimate the extracellular concentration, amantadine was determined in microdialysates in the rat striatum. At behaviorally active doses, amantadine concentration in striatal microdialysates ranged between 6 and 21 microM. These results indicate that extracellular concentrations of amantadine (CSF and serum values in patients, striatal microdialysates in the rat) are in the range of its Ki-value at the PCP binding site. Amantadine concentrations in brain tissue are much higher, probably due to intralysosomal accumulation.

Chloroquine induces human macrophage killing of Histoplasma capsulatum by limiting the availability of intracellular iron and is therapeutic in a murine model of histoplasmosis

We investigated the role of intracellular iron on the capacity of Histoplasma capsulatum (Hc) yeasts to multiply within human macrophages (Mphi). Coculture of Hc-infected Mphi with the iron chelator deferoxamine suppressed the growth of yeasts in a concentration-dependent manner. The effect of deferoxamine was reversed by iron-saturated transferrin (holotransferrin) but not by iron-free transferrin (apotransferrin). Chloroquine, which prevents release of iron from transferrin by raising endocytic and lysosomal pH, induced human Mphi to kill Hc. The effect of chloroquine was reversed by iron nitriloacetate, an iron compound that is soluble at neutral to alkaline pH, but not by holotransferrin, which releases iron only in an acidic environment. Chloroquine (40-120 mg/kg) given intraperitoneally for 6 d to Hc-infected C57BL/6 mice significantly reduced the growth of Hc in a dose-dependent manner. At 120 mg/kg there was a 17- and 15-fold reduction (P < 0.01) in CFU in spleens and livers, respectively. The therapeutic effect of chloroquine also correlated with the length of treatment. As little as 2 d of chloroquine therapy (120 mg/kg), when started at day 5 after infection, reduced CFU in the spleen by 50%. Treatment with chloroquine for 10 d after a lethal inoculum of Hc protected six of nine mice; all control mice were dead by day 11 (P = 0.009). This study demonstrates that: (a) iron is of critical importance to the survival and multiplication of Hc yeasts in human Mphi; (b) in vitro, chloroquine induces Mphi killing of Hc yeasts by restricting the availability of intracellular iron; and (c) in vivo, chloroquine significantly reduces the number of organisms in the spleens and livers of Hc-infected mice and can protect mice from a lethal inoculum of Hc yeasts. Thus, chloroquine may be effective in the treatment of active histoplasmosis and also may be useful in preventing relapse of histoplasmosis in patients with acquired immunodeficiency syndromes.

Receptor-mediated endocytosis of a manganese complex of transferrin into neuroblastoma (SHSY5Y) cells in culture

Exposure to manganese compounds often occurs as the result of industrial production or mining. Although manganese appears in traces in animal and human tissue and is essential to certain biological processes, it is also toxic. In humans and animals, toxicity is mainly associated with the nervous system. The mechanism underlying behavioral and biochemical alterations observed after manganese intoxication is not fully understood. We have shown that the manganese present in serum after exposure to manganese oxide is bound to transferrin as trivalent manganic ion. In this study of manganese uptake and storage we used a clone of human neuroblastoma cells (SHSY5Y). These cells differentiate and express catecholaminergic properties. Saturation binding analysis of the transferrin-manganese complex to the cells revealed a single class of binding sites, with an apparent KD of 13 +/- 1 nM and a density of 11,000 +/- 2,000 binding sites per cell. The complex was internalized in a temperature-dependent way and reached saturation after 2 h when approximately 2% of the added manganese had been internalized. About 80% of the internalized manganese was found in ferritin after 24 h of exposure. The results demonstrate that the transferrin receptor on SHSY5Y cells can bind and internalize a manganese-transferrin complex as efficiently as an iron-transferrin complex, although a saturation of the manganese uptake was achieved.

Chloroquine inhibits the intracellular multiplication of Legionella pneumophila by limiting the availability of iron. A potential new mechanism for the therapeutic effect of chloroquine against intracellular pathogens

Chloroquine and ammonium chloride, by virtue of their basic properties, have been shown to raise endocytic and lysosomal pH and thereby interfere with normal iron metabolism in a variety of cell types, including mononuclear phagocytes. Cellular iron metabolism is of critical importance to Legionella pneumophila, an intracellular bacterial pathogen whose capacity to multiply in human mononuclear phagocytes is dependent upon the availability of intracellular iron. In view of this, we have studied the effects of chloroquine and ammonium chloride on L. pneumophila intracellular multiplication in human monocytes. Chloroquine, at a concentration of 20 microM, and ammonium chloride, at a concentration of 20 mM, inhibited L. pneumophila intracellular multiplication by 1.4 +/- 0.2 (SEM) logs and 1.5 +/- 0.2 logs, respectively. Chloroquine- and ammonium chloride-induced inhibition of L. pneumophila intracellular multiplication was completely reversed by iron nitrilotriacetate, an iron compound which is soluble in the neutral to alkaline pH range, but not by iron transferrin, which depends upon acidic intracellular conditions to release iron. Chloroquine had no major direct effect on L. pneumophila multiplication in artificial media except at extremely high concentrations (15,000-fold that which inhibited L. pneumophila multiplication in mononuclear phagocytes), and inhibition at such concentrations was not reversed by iron nitrilotriacetate. This study demonstrates that chloroquine and ammonium chloride inhibit the intracellular multiplication of L. pneumophila by limiting the availability of iron to the bacterium. It is possible that such a mechanism of action underlies chloroquine's antimicrobial effect against other intracellular pathogens, such as the agents of malaria and tuberculosis.

Transferrin binding by mammalian cortical cells

Predominantly neuronal (neuronal) or non-neuronal (glial) cerebral cortical cell cultures were employed to study the kinetics and changes with maturation of 125I-diferric-transferrin uptake. The diferric-transferrin association curve of neuronal cultures at 37 degrees C was nonphasic and indicated equilibrium at 90 minutes. Dissociation was completed by 70 minutes. Diferric-transferrin specific uptake (80% of total) in neuronal cells (evaluated at days 6, 9, 13, 16, and 23 in culture) increased with maturation. Scatchard transformation of the data revealed increasing Bmax from day 6 to day 16 in culture (1626 to 2740 fmoles/mg protein). However, the K uptake was statistically unchanged over time and equaled 48.7 +/- 13.9 nM (mean +/- SD). In contrast, association studies of glial cultures documented equilibrium by 45 minutes and dissociation by 40 minutes. The concentration curves for diferric-transferrin uptake in glial cells, evaluated at days 11, 15, and 18 in culture, revealed virtually identical uptake at the three ages studied, but the percent specific uptake (58%) was less than for neurons (88%). Scatchard transformation of the data revealed no statistical alteration of Bmax or K uptake from days 11 to 18 in culture. Bmax ranged from 595 to 751 fmol/mg protein; overall K uptake was 48.3 +/- 13.2 nM (mean +/- SD).